This commit adds support for detecting the target WebHandler along with
WebFilters, WebExceptionHandlers, and other spring-web reactive
strategies in an ApplicationContext.
WebReactiveConfigurationSupport has @Bean factory methods for
DispatcherHandler and ResponseStatusExceptionHandler.
WebHttpHandlerBuilder has a static factory method that initializes the
builder from an ApplicationContext. This method is also used in the
DispatcherHandler#toHttpHandler(ApplicationContext) shortcut method.
Issue: SPR-14837